High variation in Eastern Whip-poor-will home-range size and shape limits the effectiveness of one-size-fits-all habitat protection methods

Abstract

Sustainable forestry harvest requires a balance between resource extraction and the habitat needs of wildlife. The breeding habitat of threatened birds is often delineated for protection by surveying sites for nesting pairs and applying fixed habitat-protection buffers around any observations. The buffers are then expected to provide sufficient habitat to complete breeding. Selecting appropriate buffer sizes requires accurate characterization of species’ habitat requirements, but the accuracy of such data varies depending on the collection method. In harvested, public forests in Ontario, Canada, current buffers used to protect Eastern Whip-poor-wills ( Antrostomus vociferus ) are informed by estimates of territory and home-range size based on call surveys or radio-telemetry. To assess the effectiveness and efficiency of these buffer sizes, we GPS-tracked 32 male Whip-poor-wills during the breeding season and estimated home ranges using continuous-time movement models. Home ranges were highly variable in size and shape, ranging from 6.8 to 135.8 ha (mean 53.6 ha). We evaluated potential ecological determinants of home range size, and found that density of forest edge and density of neighboring birds were weakly negatively related to home-range sizes. Distance to wetland and primary productivity (NDVI) were weakly positively related. We also tested how well potential buffers would protect the empirically measured home ranges by overlaying an array of variously sized buffers around simulated Whip-poor-will observations. We found that circular buffers of 50 ha (approximately the mean home-range size) would protect about 60% of an actual average home range, and 100-ha buffers (twice the mean home-range size) would be required to achieve 80% protection. Conversely, over half of the area in the simulated 50- and 100-ha buffers would protect habitat (i.e., limit forestry activity) outside of the known home range. Our results highlight the challenges, and necessity, of creating evidence-informed, broadly applicable protection measures for threatened species that rely on forested landscapes.

Keywords

• aerial insectivore
• avian conservation
• forest management
• kernel density estimators
• nightjar
• prey availability
• species at risk